On the removal time of aerosol particles from the atmosphere by precipitation scavenging

Abstract

A statistical investigation is presented on the distribution of dry and precipitation periods at a Swedish station. It is shown that the expected length of time from an arbitrary moment to the onset of the next precipitation period is about 90 and 35 hours for summer and winter conditions respectively. Based on the results of these investigations we have derived expressions for the expected length of life of an aerosol particle in the lower layers of the troposphere. Estimates of effective precipitation scavenging coefficients give expected lengths of life of the order 100–300 hours in summer and 35–80 hours in winter. The connection between the distribution of the length of life of particles in the atmosphere and the distribution of particles on the ground away from a source, is discussed and the importance of studying such age distributions is emphasized.